var readline = require('readline-sync')
readline.setDefaultOptions({ prompt: '' })
var readline = readline.prompt
let n = parseInt(readline()) // 读出n转成整数
let res = 1
for (let i = 1; i <= n; i++) {
  res *= i
}
let arr = ('' + res).split('')
let count = 0
for (let i = 0; i < arr.length; i++) {
  if (arr[i] == '0') {
    count++
  }
}
console.log(count)